1. Field of the Invention
The present invention relates to encryption in scalable video coding (SVC), and more particularly to a scalable video encryption method for maintaining a scalability function during the encryption and decryption processes, and a method for conditional access control of a specific bitstream in a scalable video bitstream based on the scalable video encryption method.
2. Description of the Related Art
Scalable video coding (SVC), which is a newly introduced concept, includes spatial scalability, temporal scalability, and quality scalability. According to the spatial scalability, an image is divided into a base layer (e.g. standard-definition television) having a lower spatial resolution and an enhancement layer (e.g. high-definition television) having a higher spatial resolution. The base layer is first encoded, and a difference component between an interpolation component of the base layer and the enhancement layer is encoded, thereby transmitting two encoded bitstreams together. When an image having been subjected to such a process is transmitted, a standard-definition television can display a broadcast for high-definition televisions based on its own screen quality by decoding a base-layer bitstream, while a high-definition television can reproduce a high-definition image by decoding both bitstreams. A digital television and a high-definition television can receive both digital television broadcast and high-definition television broadcast, thereby having complete compatibility with each other.
Similar to spatial scalability, the temporal scalability and quality scalability divide an image into a base layer and an enhancement layer, and transmit an encoded bitstream of the base layer and an encoded bitstream of a difference component between an expanded component of the base layer and the enhancement layer. However, in the case of the temporal scalability and quality scalability, there is a difference in that the temporal scalability divides a base layer and an enhancement layer along a time axis (i.e. in a screen progressing direction), and the quality scalability divides a base layer and an enhancement layer based on resolutions in bit expression for each pixel.
An SVC method capable of ensuring a Quality of Service (QoS) when a video is transmitted based on H.264/MPEG-4 AVC is being standardized by the Joint Video Team (JVT) of ITU-T and ISO/IEC. Such an SVC method shows superior adaptability when various access consumes a video, which cannot be provided by the existing coding schemes.
According to the existing MPEG-4 coding technology, a transcoding process is required whenever it is necessary to adapt contents to a different terminal, and also a very complex adaptation process and a large-capacity server are required for adapting the contents to various terminals. In contrast, according to the SVC method currently being standardized, once a video stream has been encoded, it is possible to make various videos having different spaces, times, and qualities by extracting a desired video stream from the encoded video stream without performing a re-encoding process.
This is because an encoded bitstream has a structure capable of being enhanced in space, time, and quality, as described above, and because video data for various services can be easily created through a bitstream extraction process. A bitstream having such a new structure requires a video encryption scheme suitable for the new structure.
The Intellectual Property Management and Protection (IPMP) of the Moving Picture Expert Group (MPEG) is currently engaged in research to standardize the protection of video content, and various services and encryption schemes according to the IPMP standard have been provided. However, there is only minimum research being conducted with respect to the encryption of a scalable video. Moreover, even scalable video encryption schemes researched until now support only a restricted scalable factor, and do not completely support multidimensional scalability for space, time, and quality.
Therefore, there is a need to develop an encryption method which enables conditional access to a multidimensional scalable video so as to encrypt and decrypt a specific bitstream based on a scalability function, while maintaining the entire scalability function for a scalable video supporting the complete multidimensional scalability for time, space, and quality.